Continued advances in computer technology increase interest in and demand for high data rate (e.g., >1 Gbps) wireless communication. These high data rate communications are often realized through the use of wide bandwidths. For example, Gbps data rates are often accomplished using several hundred MHz or several GHz of bandwidth. These large bandwidths are available around higher carrier frequencies such as the unlicensed 60 GHz band. FIG. 1 depicts an example 60 GHz frequency channel plan 30. The plan offers four channels 32 of about 2 GHz each centered near 60 GHz. While wide bandwidth channels offer opportunities for large data rates, they are often vulnerable to delay dispersion (delay spread) even at low range (e.g., less than 10 meters).
There are a wide variety of applications that can take advantage of wireless communications. Two pervasive applications are high data rate at large range applications and low/moderate data rate at short range applications. These applications have their own advantages and disadvantages.
In a high data rate at large range application, high data rates are achieved, but the system may have to tolerate a high delay spread. High delay spreads increase complexity and power requirements in transmitters and receivers. The higher complexity circuitry tends to have larger space requirements than short range devices, and the higher power needs are more suited for electrical plug-in devices as opposed to battery devices. In contrast, low/moderate data rate applications at a short range may be line-of-sight applications having a short delay dispersion and lower power requirements. These applications may be realized more easily in lower complexity handheld portable wireless systems that are often sensitive to power consumption.
FIGS. 2A and 2B depict block diagrams of a single carrier transmitter 40 and a single carrier receiver 50, respectively. In FIG. 2A, an encoder 42 receives input data 44 and encodes the data for transmission. The output of the encoder 42 is propagated to a single carrier modulator 46 that integrates the encoded data onto a single carrier for transmission over an antenna 48. In FIG. 2B, the receiver 50 receives single carrier wireless signals via an antenna 52 and propagates the received signals to a single carrier demodulator 54. The single carrier demodulator 54 extracts data from the received single carrier signal and passes the extracted data to a decoder 56. The decoder 56 decodes the extracted data and makes the decoded data 58 available to downstream circuitry.
FIGS. 3A and 3B depict block diagrams of a multiple carrier transmitter 60 and a multiple carrier receiver 70, respectively. In FIG. 3A, an encoder 62 receives input data 64 and encodes the data for transmission. The output of the encoder 62 is propagated to a multiple carrier modulator 66 that integrates the encoded data onto multiple carriers for transmission over an antenna 68. In FIG. 3B, the receiver 70 receives multiple carrier wireless signals via an antenna 72 and propagates the received signals to a multiple carrier demodulator 74. The multiple carrier demodulator 74 extracts data from the received multiple carrier signals and passes the extracted data to a decoder 76. The decoder 76 decodes the extracted data and makes the decoded data 78 available to downstream circuitry.
Data modulation schemes tend to be more compatible with some applications than others. For example, orthogonal frequency-division multiplexing (OFDM) is a multiple carrier multiplexing scheme that is suitable for sustaining high data rates in channels having a large delay due to the ease of frequency domain channel equalization. This makes OFDM compatible with the high data rate at large range application described above, as OFDM offers relatively simple equalization in a high delay spread channel, supports a longer range, and supports needed high data rates.
OFDM disadvantages, however, include a relatively high hardware complexity and low power efficiencies. In a wideband system having a high carrier frequency, such as 60 GHz, power amplifier (PA) efficiency at the transmitter, and analog-to-digital converter (ADC) bit-width at the receiver are engineering design challenges. Additionally, OFDM introduces high peak-to-average-ratio (PAPR) in the transmitted and received signal waveforms, requiring large headroom for the operating point at the power amplifier and analog-to-digital converter, which may reduce power amplifier efficiency and increase the complexity of analog-to-digital converter design.
It should be noted that the terms multiple carrier (MC) and OFDM modulation will be discussed throughout this disclosure and are in most cases interchangeable. Thus, where OFDM is referenced, other multiple carrier modulation techniques may be used. Similarly, references to multiple carrier modulations include OFDM implementations.
FIGS. 4A and 4B depict block diagrams of an OFDM transmitter 80 and an OFDM receiver 90, respectively. In FIG. 4A, an encoder 82 receives input data 84 and encodes the data for transmission. The output of the encoder 82 is propagated to an OFDM modulator 86 that integrates the encoded data onto multiple carriers for transmission over an antenna 88. In FIG. 4B, the receiver 90 receives OFDM wireless signals via an antenna 92 and propagates the received signals to an OFDM demodulator 94. The MC demodulator 94 extracts data from the received OFDM signal and passes the extracted data to a decoder 96. The decoder 96 decodes the extracted data and makes the decoded data 98 available to downstream circuitry.
In line of sight channels or other applications requiring lower data rates, a single carrier (SC) modulation with a time-domain equalizer is often sufficient. A single carrier system may offer simplicity in hardware combined with low power requirements and high transmit power efficiency. Single carrier modulation may present a constant envelope and/or low peak-to-average ratio easing power amplifier and analog-to-digital converter design. However, single carrier systems typically require complicated equalizers for high delay spread channels, effectively limiting the range for high data rate transfers.